Studies in defined populations in California and Western Australia, and the NCPP, have observed an excess of neurologic morbidity in children born of multiple gestations. Since multiple gestations are increasing in developed countries due to assistive reproductive interventions, and cerebral palsy in twins and triplets now contributes a larger proportion of total cerebral palsy than in the past, we have undertaken a large international study of this problem. Dr. Beverly Petterson of the University of Western Australia was in the NEB for six months during this fiscal year, and has assembled ten datasets, from Sweden, Scotland, from Oxford, Bristol, London, and the Mersey region of Britain, and Victoria, and South Australia, in addition to the California and Western Australian data, a total of 10 datasets and about 2.5 million livebirths among whom we anticipate there will be about 400 children born of multiple gestations who have cerebral palsy. Work to date has established that indeed multiple births have increased during the decade of the 1980s, and that unlike-sex pairs have increased among total twins, consistent with the view that it is pharmacologic and other medical interventions for conception (which techniques produce chiefly dizygotic twins) that have been associated with the increase in twinning and in higher order multiple births. Assembling and preparing this large multiple dataset for analysis are still underway. Dr. Petterson presented preliminary data at an international meeting on twins in Richmond, VA, in June, 1995.Dr. Jonas Ellenberg, who has left the NICHD, will continue to participate in preparation and analyses of these data. Upon her return to Western Australia, Dr. Petterson will work to finish the assembling of the data and will return to the NEB for a month early in 1996 to complete this project and prepare manuscripts describing the results.